1. Field of the Invention
The present invention relates to a terminal used for various electric and electronic devices such as an electroacoustic transducer and parts thereof and a method of forming the same.
2. Description of the Prior Art
FIG. 10 shows the structure of a terminal of a general electroacoustic transducer. This electroacoustic transducer is used for a buzzer, etc. and includes an outer casing 102 and a printed board 104 installed therein. A pair of terminals 106 are fixed to the printed board 104 and they are individually electrically connected to a wiring conductor on the printed board 104 by way of solder 108. Each terminal 106 forms an input terminal through which an ac signal etc. is applied to the electroacoustic transducer to drive the same.
For example, a terminal as shown in FIG. 11A has been used as each terminal 106 so far. This terminal includes a columnar terminal body 110, a large diameter portion 112 formed on the terminal body 110 adjacent to a rear end thereof and a conductive plating layer 116 formed on the surface of a base material 114 thereof. The large diameter portion 112 is forced into a through hole 118 formed on the printed board 104 and fixed thereto as shown in FIG. 11B. A conductive pattern 119 is formed on the surface of the printed board 104, and the terminal body 110 and the conductive pattern 119 are electrically connected to each other by way of the solder 108 as shown in FIG. 11C. However, the solder 108 flows over a region denoted at a to a region as denoted at b, which sometimes forms a solder fillet. Formation of such a solder fillet enlarges a solder adhering portion over a region which is extremely unstable in area depending on temperature, characteristic of a soldering iron, an operator's skill, etc., to cause the deterioration of quality of a product and the prevention of thinning the same such as the electroacoustic transducer, etc. This also narrows a possible soldering region for connection to an external device on the terminal body 110. Such a terminal is inserted into the through hole 118 of the printed board 104 and fixed thereto at the large diameter portion 112 alone, which causes such inconvenience that it is low in fixing strength between the printed board 104 and itself to be inferior in reliability.
A terminal as shown in FIG. 12A includes the terminal body 110 having a flange 120 and a fixing portion 122 thereunder. This terminal also has the conductive plated layer 116 on the surface of the base material 114 thereof. As shown in FIG. 12B, such a terminal is fixed to the printed board 104 in such a way that firstly the fixing portion 122 is inserted into the printed board 104, secondly the terminal body 110 is positioned perpendicular with respect to the printed board 104 by way of the flange 120, thirdly the end of the fixing portion 122 is crushed to fix the terminal body 110 to the printed board 104, and finally the terminal body 110 and printed board 104 are fixedly connected to each other by the solder 108. The terminal having the flange 120 has such effects that it is easily positioned and has high fixing strength with respect to the printed board 104. Even in case of such a terminal, however, when it is subjected to soldering using a soldering iron, a solder 108' flows over the peripheral surface of the flange 120 to adhere to the upper surface of the same at the terminal body 110 side to form a solder fillet there as shown in FIG. 12C. Such solder 108' is unnecessary and also causes deterioration of the product, prevents the product from being thinned and reduces the solder 108 at a portion where soldering is essentially necessary.
Such adhesion of the solder 108' is closely related with the forming process of the terminal. FIG. 13A, FIG. 13B and FIG. 13C show the forming process of a terminal according to a general manufacturing method thereof.
A rod-shaped base material 114 is used for the terminal material and a smooth-surfaced conductive plating layer 116 is formed on the surface thereof. The terminal material is previously cut in a given length in accordance with a mold, then inserted into the molds 124 and 126 and is subjected to a pressure molding process in cavities 128 and 130 of the molds 124 and 126 respectively. The pressure molding process will be described hereinafter sequentially. In a step of FIG. 13A, the compressed base material 114 is swelled in the cavities 128 and 130 to form the flange 120, wherein the molding process is gently performed in this step so that the conductive plating layer 116 is also swelled along the surface of the flange 120. When the molding process advances from the step of FIG. 13A to a step of FIG. 13B, the conductive plating layer 116 in the peripheral surface portion of the flange 120 is cracked to expose the base material 114 thereunder. In a last step as shown in FIG. 13C, an exposed portion 132 of the base material 114 appears on a peripheral wall portion of the flange 120, thereby forming the terminal as shown in FIG. 12A. The surface of the exposed portion 132 of the base material 114 is uneven so that it is inferior in solder wetting.
It is a matter of course that the conductive plating layer 116 is a means to enhance solder wetting performance. A portion where the base material 114 is exposed from the conductive plating layer 116, namely, the exposed portion 132 is extremely reduced in solder wetting performance. As a result, most solder flows toward the solder 108' as shown in FIG. 12C, which causes not only the deterioration of quality but also the connection failure of the solder 108 between the terminal body 110 and the printed board 104.
A terminal as shown in FIG. 14A has been also used as the terminal 106 so far. The terminal of this type has flanges 134 and 136 forming a stepped flange on the terminal body 110. In such a terminal, the conductive plating layer 116 is also formed on the surface of the base material 114. As shown in FIG. 14B, the terminal 106 is fixed to the printed board 104 in such a way that firstly the fixing portion 122 is inserted into the printed board 104, secondly the terminal body 110 is positioned perpendicular with respect to the printed board 104 by way of the flange 134, thirdly the end of the fixing portion 122 is crushed to fix the terminal body 110 to the printed board 104, and finally the terminal body 110 and printed board 104 are fixedly connected to each other by the solder 108. Accordingly, the terminal 106 has such effects that it is easily positioned and firmly fixed to the printed board 104. However, such a terminal also has the same drawbacks as the terminal as shown in FIG. 12 that the solder 108' flows over the peripheral surfaces of the flanges 134 and 136 to adhere to the surface of the flange 136 at the terminal body 110 side. Further, the flanges 134 and 136 constitute a step-structure which increases the thickness of the terminal 106, causing such an inconvenience that the thermal 106 is prevented from being miniaturized.
Such adhesion of the solder 108' is caused by the same reason as that described relating to the terminal of FIG. 12. FIG. 15A, FIG. 15B and FIG. 15C show the molding processes of the terminal. The terminal material is previously cut in a given length, then inserted into the molds 124 and 126 and is subjected to a pressure molding process in cavities 128 and 130 of the molds 124 and 126 respectively. In each step of the molding process, the compressed base material 114 is swelled in the cavities 128 and 130 to form the flanges 134 and 136, the conductive plating layer 116 on the peripheral surface portion of the flanges 134 and 136 are cracked so as to expose the base material 114 thereunder. Exposed portions 138 and 140 of the base material 114 are lower than the surface of the conductive plating layer 116 in solder wetting performance, so that the solder 108' moves toward a portion having high solder wetting performance as shown in FIG. 14C, which results in reduction of the solder 108 at a necessary soldering portion to lower the adhesive strength.